Celine performed her 1,144th show Saturday night at the Colosseum at Caesars Palace ... where the crowd caught all the feels -- but at one point she delayed the show for one special fan's bathroom break.

She noticed him getting up, and waited until he returned to his front-row seat to restart the show. Celine joked it was the least she could do, considering he was probably broke after dropping big money on 2 tickets to the big Vegas finale. She also practiced good hygiene ... watch the clip.

That aside, Celine called the show "bittersweet" and said she never imagined doing so many shows in Vegas when she started on March 25, 2003.

At the end of the show, her 3 sons brought her roses and joined Mom for a final bow to a massive standing ovation.

Au revoir, Celine. C'est magnifique!!!